IC Engine Questions and Answers – Engine Efficiencies

1. The ratio of the heat equivalent to one kW hour to the heat in fuel per B.P. hour is termed as brake thermal efficiency.
a) True
b) FalseView Answer

Answer: a
Explanation: Brake thermal efficiency is defined as the ratio of the heat equivalent to one kW hour to the heat in fuel per B.P. hour.

2. The ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time is called
a) mechanical efficiency
b) overall efficiency
c) indicated thermal efficiency
d) volumetric efficiencyView Answer

Answer: b
Explanation: Overall efficiency is the ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time while mechanical efficiency is the ratio of the brake power to the indicated power and relative efficiency is the ratio of the indicated thermal efficiency to the air standard efficiency.

3. The ratio of the brake power to the indicated power is called
a) mechanical efficiency
b) overall efficiency
c) indicated thermal efficiency
d) volumetric efficiencyView Answer

Answer: a
Explanation: Mechanical efficiency is the ratio of the brake power to the indicated power and relative efficiency is the ratio of the indicated thermal efficiency to the air standard efficiency whereas overall efficiency is the ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time.

4. The ratio of the indicated thermal efficiency to the air standard efficiency is known as
a) mechanical efficiency
b) overall efficiency
c) relative efficiency
d) volumetric efficiencyView Answer

Answer: c
Explanation: Relative efficiency is the ratio of the indicated thermal efficiency to the air standard efficiency whereas overall efficiency is the ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time and mechanical efficiency is the ratio of the brake power to the indicated power.

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5. The correct sequence of the decreasing order of brake thermal efficiency of the three given basic types of engines is
a) four stroke C.I. engine, four stroke S.I. engine, two stroke S.I. engine
b) four stroke S.I. engine, four stroke C.I. engine, two stroke S.I. engine
c) four stroke C.I. engine, two stroke S.I. engine, four stroke S.I. engine
d) two stroke S.I. engine, four stroke S.I. engine, four stroke C.I. engineView Answer

Answer: a
Explanation: The brake thermal efficiency of the three given basic types of engines decreases in the order four stroke C.I. engine, four stroke S.I. engine, two stroke S.I. engine.

6. The brake power of a diesel engine, keeping other parameters constant, can be increased by
a) decreasing the density of intake air
b) increasing the temperature of intake air
c) increasing the pressure of intake air
d) decreasing the pressure of intake airView Answer

Answer: c
Explanation: By increasing the pressure of intake air, the brake power of a diesel engine, keeping other parameters constant, can be increased and by no other means.

Answer: b
Explanation: In actual working, as compared to air standard cycle, the effect of variation in specific heats is to decrease maximum pressure and maximum temperature.

9. The ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston is called
a) mechanical efficiency
b) overall efficiency
c) relative efficiency
d) volumetric efficiencyView Answer

Answer: d
Explanation: Volumetric efficiency is the ratio of the volume of charge admitted at N.T.P. to the swept volume of the piston while mechanical efficiency is the ratio of the brake power to the indicated power and relative efficiency is the ratio of the indicated thermal efficiency to the air standard efficiency whereas overall efficiency is the ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time.

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10. The overall efficiency is defined as the ratio of the work obtained at the crankshaft in a given time to the energy supplied during the same time.
a) True
b) FalseView Answer

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